Dempsey L A, Zhao A C, Khan S A
Department of Molecular Genetics and Biochemistry, University of Pittsburgh School of Medicine, Pennsylvania 15261, USA.
Mol Microbiol. 1995 Feb;15(4):679-87. doi: 10.1111/j.1365-2958.1995.tb02377.x.
A number of small, multicopy plasmids from Gram-positive bacteria replicate by an asymmetric rolling-circle mechanism. Previous studies with several of these plasmids have identified a palindromic sequence, SSOA, that acts as the single-strand origin (SSO) for the replication of the lagging-strand DNA. Although not all the SSOA sequences share DNA sequence homology, they are structurally very similar. We have used an in vitro system to study the lagging-strand replication of several plasmids from Gram-positive bacteria using the SSOA sequences of pT181, pE194 and pSN2 as representative of three different groups of Staphylococcus aureus plasmids. In addition, we have investigated the lagging-strand replication of the pUB110 plasmid that contains an alternative single-strand origin, SSOU. Our results confirm that RNA polymerase is involved in lagging-strand synthesis from both SSOA and SSOU-type lagging-strand origins. Interestingly, while initiation of lagging-strand DNA synthesis of pUB110 occurred predominantly at a single position within SSOU, replication of pT181, pSN2 and pE194 plasmids initiated at multiple positions from SSOA.
一些来自革兰氏阳性菌的小型多拷贝质粒通过不对称滚环机制进行复制。此前对其中几种质粒的研究已鉴定出一个回文序列，即单链起始位点（SSOA），它作为滞后链DNA复制的单链起始位点。尽管并非所有的SSOA序列都具有DNA序列同源性，但它们在结构上非常相似。我们利用体外系统，以pT181、pE194和pSN2的SSOA序列作为金黄色葡萄球菌三种不同质粒组的代表，研究了几种革兰氏阳性菌质粒的滞后链复制。此外，我们还研究了含有另一种单链起始位点SSOU的pUB110质粒的滞后链复制。我们的结果证实，RNA聚合酶参与了来自SSOA和SSOU型滞后链起始位点的滞后链合成。有趣的是，虽然pUB110滞后链DNA合成的起始主要发生在SSOU内的单个位置，但pT181、pSN2和pE194质粒的复制从SSOA的多个位置起始。
